http://www.youtube.com/watch?v=J4hft34WRYw

Yeah, someone found a soundclip in half-life that has the same dialouge too. The problem is, what is combine dialouge doing in a soundwave for the next portal game?

Portal gun = reflect combine bullets.

Simple. Either this is actually a setup for Episode 3 or Portal 2 will involve the Combine.

or both

combine dialogue is in portal cuz the combine are cool